<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 240px;
            height: 150px;
            background-color: khaki;
        }
        .box .item{
            width: 50px;
            height: 50px;
            background-color: skyblue;
            margin: 10px;
            float: left;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="item b1">1</div>
        <div class="item b2">2</div>
        <div class="item b3">3</div>
        <div class="item b4">4</div>
    </div>
</body>
</html>